1. Field of the Invention
This invention relates to the manufacture of edible food casings derived from animal hide collagen and more particularly to an improved method of preparing extrudable collagen compositions.
2. The Prior Art
Collagen casings have been widely accepted as edible food casings for pork sausages. In the preparation of edible collagen casings, hide collagen derived from animal hides is converted into a finely divided fibrillar form and extruded in tubular form to form the casing. There are basically two processes for forming the casings.
In the first of these processes, referred to in the art as the "slurry" process, collagen derived from finely comminuted animal hides is suspended in an aqueous bath at a low solids content, i.e., 2.0-6% by weight and about 1 to 4% by weight of a weak organic acid having a dissociation constant in the order of about 1 .times. 10.sup..sup.-6 to about 1 .times. 10.sup..sup.-3 in water at 25.degree. C such as lactic acid, is added to the bath to adjust the pH of the bath to a range of about 2.5 to 3.7 to swell the collagen and form collagen fibrils. The dilute slurry of swollen collagen fibrils is extruded as a tubular mass into a concentrated sodium sulfate or aluminum sulfate coagulating bath which dehydrates the collagen slurry and forms coherent tubing. The tubing is then passed through a tanning bath, e.g. a bath containing a hardening agent such as alum to form a handlable casing. The hardened tubing is then washed to remove entrained salts and inflated and dried to form the desired casing product. The slurry process is completely disclosed in U.S. Pat. Nos. 3,123,482, 3,194,865 and 3,413,129.
The second of the basic processes for forming collagen casings is referred to in the art as the "dough" process. In the dough process as disclosed in U.S. Pat. No. 2,114,220, hide fragments are swelled with a dilute (1-5%) aqueous solution of an alkaline substance such as Ca(OH).sub.2 or an acid substance such as HCl and the swelled hide fragments are comminuted into a collodial paste containing 10-20% collagen solids. The paste adjusted to a pH of 2.5-3.5 is extruded under high pressure (350-450 atms) directly into tubing which is then dried to form the desired collagen casing product.
In the slurry process the use of weak acids such as lactic acid is an appreciable cost factor in the manufacture of the casing and a portion of the lactic acid from the extruded slurry eventually finds its way into the process effluent which must be removed therefrom as its organic nature creates a pollution problem. It would be beneficial in terms of cost and in the alleviation of pollution problems that the amount of lactic acid used in the slurry process be reduced.